Field of the Invention
The present invention relates to a light source unit and a projector including this light source unit.
Description of the Related Art
In these days, projectors (projecting systems) are used on many occasions which project a screen of a personal computer and a video image, as well as images based on image data which is stored on a memory card on to a screen. These projectors are such that light emitted from a light source is collected on to a micromirror display device called a digital micromirror device (DMD) or a liquid crystal panel, so that a color image is projected on to a screen for display thereon.
The application of these projectors is expanded from a presentation in a business scene to a domestic use in association with the propagation of personal computers and video equipment such as DVD players. Conventionally, the mainstream of these projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been made developments of various types of projectors which use, as a light source, a plurality of semiconductor light emitting devices such as laser diodes and which include a luminescent plate which uses the semiconductor light emitting devices as an excitation light source.
A projector disclosed in Japanese Unexamined Patent Application No. 2015-45673 (JP-A-2015-45673) includes a red light source device including a red light emitting diode and a luminescent plate device having a luminescent plate such as a luminescent wheel having a luminescent material layer and a diffuse transmission area. The luminescent material layer receives light in a blue wavelength range emitted from an excitation light shining device including blue laser diodes as excitation light to emit luminous light in a green wavelength range. The diffuse transmission area transmits light emitted from the excitation light shining device while diffusing the light. The excitation light shining device also functions as a blue light source, for light emitted therefrom is transmitted diffusely through the diffuse transmission area of the luminescent plate.
Then, the excitation light shining device and the red light source device are disposed so that light emitted from the former device intersects light emitted from the latter device at right angles. A dichroic mirror is disposed in a position where light emitted from the excitation light shining device and light emitting from the red light source intersect each other at right angles. Light emitted from the excitation light shining device is transmitted through the dichroic mirror to be shone on to the luminescent plate device. On the other hand, light emitted from the red light source device is also transmitted through the dichroic mirror. Luminous light which is light emitted from the luminescent plate device is reflected by the dichroic mirror.
Here, according to the spectral characteristics of the dichroic mirror, in general, it is difficult to transmit or reflect all of light in a specific wavelength. Consequently, in the projector disclosed in JP-A-2015-45673, when light emitted from the excitation light shining device is transmitted through the dichroic mirror, there may be a case where part of the emitted light is reflected slightly by the dichroic mirror to be shone on to the red light source device. In case the projector is used over a long period of time in such a state that even a slight amount of light emitted from the excitation light shining device which uses the semiconductor light emitting devices such as laser diodes which emit highly intense light is shone on to the red light source device, there may be a case where the service life of the optical device of the red light source device is so badly affected that the service life is shortened.